The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Various techniques have been researched and developed for reducing combustion heat during combustion in an internal combustion engine of a vehicle to reduce emissions such as nitrogen oxides (NOx), and reducing a mixture ratio of air and fuel to improve fuel efficiency.
As representative techniques for reducing combustion heat and NOx emissions and improving fuel efficiency, an exhaust gas recirculation (EGR) system, a water injection system, emulsion fuel, CO2 capture and injection, and the like have been researched and developed.
The EGR system may include an EGR pipe for circulating EGR gas from an exhaust system to an intake system, an EGR cooler for cooling temperature of the EGR gas, and an EGR valve for regulating the flow of the EGR gas, so that it may occupy a relatively large installation space in a narrow engine room and the assembly cost may be increased.
In addition, the EGR system may only operate in a portion of an operating range of the vehicle and operate depending on RPM of the engine, so that the range of use of the EGR gas may be very limited. For example, the operation of the EGR system may not be smoothly performed in a low RPM region and a high RPM region of the engine.
The water injection system may be configured to spray water into the incoming air or fuel-air mixture, or directly into a combustion chamber of the engine. Water injection may lower the temperature of the combustion chamber, reduce emissions of NOx, hydrocarbons, and the like, and reduce the mixture ratio of air and fuel to thereby improve fuel efficiency.
Recently, a fuel and water injection system in which fuel and water are supplied to a single injector and the injector injects the fuel and the water together into the combustion chamber of the engine has been researched and developed.
In a conventional fuel and water injection system, however, a mixture of water and fuel remaining in the injector may be collected (circulated) in a fuel tank through a return passage connected to the injector, so that the water-fuel mixture may gradually increase in the fuel tank as the operating time elapses. We have discovered that even when the injection of fuel alone is desired in a full load operating condition, or the like, the water together with the fuel may be injected, which lowers the combustion efficiency.
The above information described in this background section is provided to assist in understanding the background of the inventive concept, and may include any technical concept which is not considered as the prior art that is already known to those skilled in the art.